Hot cathode gaseous discharge device



Dec. 18, 1934. Y. IMAOKA 1,985,096

HOT CATHODE GASEOUS DISCHARGE DEVICE Filed May 11, 1931 Ehventow:

, x oshio hnmz-koka H is Attov'neg.

Patented Dec. 18, 1934 UNITED STATES PATENT OFFICE HOT CATIIODE GASEOUSDISCHARGE DEVICE Yosliio Imaoka, Tokyo,

era] Electric Company,

Japan, assignor to-Gcna corporation oi New The present invention relatesto an electric discharge apparatus and more particularly to devicescontaining gas or vapor and which are provlded with an indirectly heatedcathode. An 6 object of the invention is to provide a device in whichthe electrical discharge is prevented from injuring a cathode of thissort by positive ion bombardment. The accompanying drawing shows anexemplary form of the improved tube.

In gaseous discharge apparatus, the negative space charge is overcome byionization, so that the tube is capable of passing relatively largecurrent. However, in these tubes, the cathode tends to becomedisintegrated by the intense bombardment of positive ions. In order toreduce this effect as much as possible, it is usual to employ ruggedcathodes of the indirectly heated type and to coat the exterior withelectron-emitting material. These cathodes contain considerable metal,hence the heat capacity is high, so that they do not attain theiroperating temperature for a considerable length of time after the heateris initially energized. In consequence, the oathode is bombarded bypositive ions and the active coating destroyed before the electronemission reaches its full value. In order to eliminate this bombardingeffect, it has been proposed heretofore to insert a relay in the anodecircuit, the

purpose of which is to retard the application of full voltage to thetube until the cathode has reached its proper operating temperature.

The present invention avoids the use of such a relay but still providessubstantial protection to the cathode from the bombarding effect of thearc stream. The improvement is particularly adapted to circuitscontaining devices which may be damaged it the full line voltage wereimpressed on the circuit and no discharge current were flowing in thetube. In brief, my invention contemplates the use of an auxiliarycathode of relatively small heat capacity which quickly reaches itsoperating temperature and carries for a short period of time, a reducedload current. This auxiliary cathode remains operative until the maincathode has reached its full load current-carrying capacity or anypredetermined portion thereof, after which the auxiliary cathodeautomatically is deenergized.

In the drawing, an anode 2, a control member 3 and an equi-potentialcathode 4 are contained within a sealed envelope. The cathode isconstituted of a metal cylinder containing a heater and is coated withalkaline earth oxide or other electron-emitting insulating material. Itis apparent that a cathode of this type has large heat capacity and maytake considerable time to attain its proper temperature for operation.The grid or control member 3 substantially encloses the cathode and isconstituted either of a perforated plate or metal mesh. The controlmember 3 and the cathode 4, which will be referred to hereinafter as themain cathode, are supported within the envelope from a reentrant stem byrigid leading-in conductors. The anode 2, consisting of metal or carbon,is supported from the opposite end of the envelope also by a leading-inconductor.

In accordance with my invention, there is provided about the maincathode 4, a helix 5 of fine wire of pure or thoriated tungsten and. theends of which are brought out through the same reentrant stem thatsupports the main cathode and the grid. Current is supplied to the maincathode and heater through conductors 6 and to the auxiliary cathodethrough conductors 7, while the controlmember and the anode obtain theirenergy through conductors 9 and 8 respectively. The envelope containsinert gas or vapor at a suitable pressure for substantially eliminatingspace charge, for example, 50 millimeters of mercury more or less.

The device is shown as connected in an exemplary circuit which includesa photo-electric tube 15 for controlling the device. The main cathode 4and the auxiliary cathode 5 are connected in parallel to a source ofheating current (not shown) respectively through the resistances l0 andii. The auxiliary cathode is designed to operate at very low voltages,e. g. below seven volts, so that the resistance 11 must be suflicientlylarge to provide the necessary drop in voltage.

The main cathode is connected to the anode through a relay 12, a sourceof electrical energy '(not shown), and a load 13, while the controlmember 3 is connected to the anode 2 through an inductance l4 and to themain cathode 4 through the photo-electric tube. The relay 12 isenergized by anode current and opens the heating circuit of theauxiliary cathode 5 when the current through the tube reaches apredetermined value, dependent upon the temperature attained by the maincathode.

It is apparent that when the auxiliary cathode is connected to itssource of current in any suitable manner, and thereafter attains itsmaximum electron-emitting condition, the impedance of the tube islowered to such an extent that current of a reduced value immediatelyflows between the anode and the auxiliary cathode. For

a short period of time, the anode current is maintained practicallyentirely by the electrons emanated from the auxiliary cathode and flowsthrough the load 13 and the relay 12. The main cathode 4 then graduallyheats up by reason of the contained heater and its emissivity increasesuntil the anode current through relay 12 is of sufllcient magnitude tocause the latter to pull up its armature, thereby opening the auxiliarycathode circuit.

The photo-electric tube represents any form of a variable resistancecontrol member or the like for cooperating withthe inductance ,14 insuch a manner as to change the phase of the voltages applied to theanode and control member, thereby varying the average value oi currentflowing through the load 13, as is well known in the art.

From the foregoing, it is evident that I have provided a novel form oftube which contains an auxiliary cathode in addition to the maincathode, the function of the auxiliary cathode being to provide a supplyof electrons immediately upon energizing the tube so that a spacecurrent is caused to flow through the tube during the time when'the maincathode is reaching its operating temperature. By reason of the improvedcathode arrangement, it is possible to employ main cathodes of high heatcapacity without being subject to excessive positive ion bombardment.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A gaseous discharge device comprising an evacuated envelopecontaining ionizable gas at a pressure suflicient to neutralize spacecharge, a plurality of electrodes therein including main and auxiliarycathodes and an anode, said main cathode being indirectly heated andsaid auxiliary cathode being in addition to the main cathode heater,said main cathode having a relatively large heat capacity and at itsnormally operating temperature adapted to carry the entire load current,and the auxiliary cathode having a relatively small heat capacity and atits normally operating temperature adapted to carry a portion only ofthe load current, said cathodes being heated independently of oneanother, and means for energizing the auxiliary cathode and raising itstemperature to the operating condition prior to raising the temperatureof the main cathode to its. operating condition.

2. A gaseous discharge device comprising an evacuated envelopecontaining ionizable gas at a pressure sufficient to neutralize spacecharge, a plurality of electrodes therein including main and auxiliarycathodes and an anode, said main cathode being indirectlyheated and saidauxiliary cathode being in addition to the main cathode heater, saidmain cathode having a relatively large heat capacity and at its normallyoperating temperature adapted to carry the entire load current, and theauxiliary cathode having a relatively small heat capacity and atitsnormally operating temperature adapted to carry a portion only of theload current, said cathodes being heated independently of one another,and means for energizing the auxiliary cathode and raising itstemperature to the operating condition prior to raising the temperatureof the main cathode to its operating condition, and means fordeenergizing the auxiliary cathode when the main cathode has reached itsoperating temperature.

3. A gaseous discharge device comprising an evacuated envelopecontaining ionizable gas at a pressure sufiicient to neutralize spacecharge, a plurality of electrodes therein including and auxiliarycathodes and an anode, said ma' cathode being indirectly heated and saidauxili cathode being in addition to the main cathode heater, said maincathode having a relatively large heat capacity and at its normallyoperating temperature adapted to carry the entire load current, and theauxiliary cathode having a rela tively small heat capacity and at itsnormally operating temperature adapted to carry a portion only of theload current, said cathodes being heated independently of one another,and means for energizing the auxiliary cathode and raising itstemperature to the operating condition prior to raising the temperatureof the main cathode to its operating condition, and means comprising arelay responsive to anode current for deenergizing the auxiliarycathode'when the main cathode has reached its operating temperature.

4. A gaseous discharge device comprising an evacuated envelopecontaining ionizable gas at a pressure sufiicient to neutralize spacecharge,

a plurality of electrodes therein including main and auxiliary cathodesand an anode, said main cathode having a relatively large heat capacityand at its normally operating temperature adapted to carry the entireload current, and the aux-' iliary cathode having a relatively smallheat capacity and at its normally operating temperature adapted to carrya portion only of the load current, said cathodes being heatedindependently of one another, and means for energizing the auxiliarycathode and raising its temperature to the operating condition prior toraising the temperature of the main cathode to its operating condition,said main cathode comprising a cylindrical member coatedwithelectronically active material and said auxiliary cathode comprising ahelix surrounding the main cathode.

YOSHIO IMAOKA.

